1. Field of the Invention
The present invention relates to a method for attaching a radar for vehicle (Radar: Radio detecting and ranging), and a radar for vehicle. In more detail, the invention relates to an attachment method for attaching onto a vehicle in a proper manner a radar for vehicle that monitors front sight and rear sight of the vehicle, and to the radar for vehicle.
2. Description of the Related Art
In a conventional system for assisting driving of vehicles, a distance between oneself and a vehicle ahead and a relative speed therebetween are measured with using radar. Also, the conventional assisting system controls the vehicle to keep the distance between oneself and the vehicle ahead based on those measurement values.
FIG. 5 is a schematic diagram showing a state where conventional radar for vehicle is used. In FIG. 5, reference numeral 1 designates the radar for vehicle. An antenna (not shown) of the radar 1 for vehicle is attached in the vicinity of a grill of a vehicle 2 or inside a bumper of the vehicle 2. The radar 1 for vehicle has sharp directivity at frequency so as to be able to detect distance, direction, and velocity of an object (for example, a vehicle ahead) that is about 80 m–100 m from the vehicle 2. The directivity of an antenna can be evaluated using an angle (half width at a half maximum of the directivity) at a position where gain becomes smaller than a peak value by 3 dB in the directivity pattern. FIG. 8 shows a horizontal directivity pattern of one antenna, and θh represents a half width at a half maximum of the directivity. Generally, an antenna having θh=about 4° in the horizontal directivity pattern is employed in radar for vehicle that detects at a distance of about 80 m–100 m. A reference numeral 1a represents a detection range of the radar 1 for vehicle.
As described above, the antenna of the radar 1 for vehicle is attached in the vicinity of the grill of the vehicle 2 or inside the bumper of the vehicle 2. That is, the antenna is attached at a low position relative close to a road surface. Therefore, a reflection wave from the road surface has great affect, so that there is a fear that the detection accuracy of the radar 1 for vehicle might degrade.
In order to solve these problems, JP-A-Hei. 6-168400 discloses the following techniques. In JP-A-Hei. 6-168400, a vertical directivity of an antenna has a downward gain, which is smaller than an upward gain, that is, is asymmetric. By employing this technique, even if an antenna of radar for vehicle is attached at a low position close to the road surface, affect of a reflection wave from the road surface can be reduced.